We are planning on replacing our 3 ft high deck with a concrete patio about 12" thick and 30 ft wide. If we had to do it we will have to pour concrete over the hardi plank siding. Talked to a couple of concrete contractors they said they will apply metal flashing and pour concrete over the siding and that it should not be a problem. Is it safe to do that? I am concerned, will it cause moisture problems in the inside of the house in the long run? Thanks for any reg. this.

First off you are using way more concrete than needed for a patio. 4' is good enough for a patio. 6" for a driveway. This would lower your patio 8" but if you need it higher use gravel. You need a better concrete guy. If he told you 12" he was taking your money and building a bomb shelter. Not a patio. Also, you don't pour up againist siding. The sliding should be removed, flashing installed and a spacer (celotex) installed.

We are planning on replacing our 3 ft high deck with a concrete patio about 12" thick and 30 ft wide. If we had to do it we will have to pour concrete over the hardi plank siding. Talked to a couple of concrete contractors they said they will apply metal flashing and pour concrete over the siding and that it should not be a problem. Is it safe to do that? I am concerned, will it cause moisture problems in the inside of the house in the long run? Thanks for any reg. this.
Thanks a lot for your reply. I had forgot to mention, it is 4" concrete and the rest will be crushed concrete. I was skeptical about removing the siding, flashing installed and a spacer (celotex) installed. Is it perfectly safe to pour concrete and gravel against this? Will it cause moisture problems inside the house after a few years? Also can you explain the purpose of celotex?

"Is it perfectly safe to pour concrete and gravel against this?" Which this, the siding or the celotex? Siding bad, celotex good. It will provide a slip joint between you home structure and the concrete pad. That pad will more ever so slightly as the seasons change but the house will not move.

We are planning on replacing our 3 ft high deck with a concrete patio about 12" thick and 30 ft wide. If we had to do it we will have to pour concrete over the hardi plank siding. Talked to a couple of concrete contractors they said they will apply metal flashing and pour concrete over the siding and that it should not be a problem. Is it safe to do that? I am concerned, will it cause moisture problems in the inside of the house in the long run? Thanks for any reg. this.
Thanks for the clarification. I meant over celotex. Does the same process of removing, flashing and spacing apply to lapbands as well? Also we will be closing up about 6 crawlspace vents from the back of our house, if we build the high patio, is it fine to do that? Do we have to install more vents else where?

You probably need more vents or add a power vent. You need air to flow and circulate to remove moisture coming up through the soil.

I Don't See A Problem With Pouring Up To The Hardi Siding, This Is The Concrete Siding Correct? As Far As Flashing, If You Had A Deck To Begin With There Should Be Flashing Already Installed Behind The Hardi Board,
And Ballengerb1 Is Right 12" Is Way Over Kill, And I Question How Youd Support That,
4" In Standard, If Your Worried About Crack You Can Have Some Fiberglass Added To It, And Yes To Vents